U.S. patent number 4,932,410 [Application Number 07/259,217] was granted by the patent office on 1990-06-12 for dual membrane mounting for transcutaneous oxygen and carbon dioxide sensor.
This patent grant is currently assigned to Novametrix Medical Systems, Inc.. Invention is credited to William J. Lacourciere, David R. Rich.
United States Patent |
4,932,410 |
Lacourciere , et
al. |
June 12, 1990 |
Dual membrane mounting for transcutaneous oxygen and carbon dioxide
sensor
Abstract
A transcutaneous sensor probe having dual sensing electrodes
responsive to the effects of two different transcutaneous gases on
an ion solution separated from the skin surface by a selectively
permeable seal having respective regions overlying the
corresponding electrodes. The permeable seal is mounted on a
removable fixation ring which is indexed to ensure alignment
between each region of the seal and its respective electrode when
the fixation ring is connected to the electrode housing.
Inventors: |
Lacourciere; William J.
(Chesire, CT), Rich; David R. (San Diego, CA) |
Assignee: |
Novametrix Medical Systems,
Inc. (Wallingford, CT)
|
Family
ID: |
22984035 |
Appl.
No.: |
07/259,217 |
Filed: |
October 18, 1988 |
Current U.S.
Class: |
600/354;
204/403.06; 204/412; 204/415; 600/357 |
Current CPC
Class: |
A61B
5/14542 (20130101); A61B 5/1477 (20130101); G01N
27/4045 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); G01N 27/49 (20060101); A61B
005/00 () |
Field of
Search: |
;128/635
;204/403,412,415 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
0088748 |
|
Jul 1980 |
|
JP |
|
0128945 |
|
Jun 1986 |
|
JP |
|
8102831 |
|
Oct 1981 |
|
WO |
|
Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Mandelbaum; Howard F.
Claims
What is claimed is:
1. A sensor for monitoring first and second transcutaneous gases at
the surface of the skin comprising,
an electrode housing,
a first electrode mounted in said electrode housing for detecting
said second gas,
a second electrode mounted in said electrode housing for detecting
said second gas,
a seal supporting housing releasably mountable on said electrode
housing, each of said seal supporting housing and said electrode
housing including a respective indexing means for limiting relative
movement therebetween,
a selectively permeable seal mounted on said seal supporting
housing, said seal having a first region permeable to said first
gas and a second region permeable to said second gas,
and cooperative interlocking means on said electrode housing and on
said seal supporting housing for positively mounting said seal
supporting housing on said electrode housing with said first region
of said seal in engagement with said first electrode and said
second region of said seal in engagement with said second
electrode, said first and second electrodes being angularly
displaced from said electrode housing indexing means by the same
degree to which said first and second permeable seal regions are
respectively angularly displaced from said seal supporting housing
indexing means.
2. A sensor for monitoring first and second transcutaneous gases at
the surface of the skin according to claim 1 wherein said
cooperative interlocking means comprises a single pitch attachment
thread on said seal supporting housing and a complimentary single
pitch attachment thread on said electrode housing.
3. A sensor for monitoring first and second transcutaneous gases at
the surface of the skin according to claim 2 wherein said seal
supporting housing indexing means comprises a first abutment and
said electrode housing indexing means comprises a second abutment
adapted to engage said first abutment for positively limiting
relative rotation therebetween.
4. A sensor for monitoring first and second transcutaneous gases at
the surface of the skin according to claim 3 wherein said first
abutment is integral with said seal supporting housing thread and
said second abutment is integral with said electrode housing
thread.
5. A sensor for monitoring first and second transcutaneous gases at
the surface of the skin according to claim 1 further comprising
elastomeric means for releasably attaching said permeable seal to
said seal supporting housing for permitting adjustment of the
relative angle between said permeable seal and said seal supporting
housing.
6. A method of preparing, for monitoring first and second
transcutaneous gases at the surface of the skin, a sensor having a
first electrode for detecting said first gas and a second electrode
for detecting said second gas comprising
mounting a selectively permeable seal having a first region
permeable to said first gas and a second region permeable to said
second gas relative to an index on a seal supporting housing
and
connecting said seal supporting housing to said sensor with said
index in a predetermined position relative to said first and second
electrodes so that said first and second electrodes are angularly
displaced from said index by the same degree to which said first
and second permeable seal regions are respectively angularly
displaced from said index, and limiting relative movement
therebetween, whereby said first and second regions of said
permeable seal are in alignment with said first and second
electrodes, respectively.
7. A method according to claim 7 wherein said seal supporting
housing is threaded onto said sensor and said index comprises the
beginning of a thread.
8. A method according to claim 7 wherein said seal supporting
housing is threaded onto said sensor and said index comprises the
terminus of a thread.
9. A method according to claim 7 wherein said seal supporting
housing is threaded onto said sensor and the beginning of the
thread on one of said sensor and said seal supporting housing
engages the terminus of the other of the thread on one of said
sensor and said seal supporting housing to positively fix the
relative angular positions of said sensor and said seal bearing
housing with said first and second regions of said permeable seal
aligned with said first and second electrodes, respectively.
Description
BACKGROUND OF THE INVENTION
This invention relates to the use of a single sensor probe and
monitor to detect and measure transcutaneous gases at the surface
of the skin. More specifically, this invention relates to a sensor
probe having dual sensing electrodes responsive to the effects of
two different transcutaneous gases on an ion solution separated
from the skin surface by a selectively permeable seal having
respective regions covering the corresponding electrodes.
It is known in the art to measure oxygen and carbon dioxide in the
blood non-invasively by measuring the partial pressures of oxygen
(pO.sub.2) and carbon dioxide (pCO.sub.2) in the adjacent body
tissue. The measurement is done by means of a transcutaneous gas
sensor having a electrodes covered by a selectively permeable seal
in the form of a membrane. In the case of oxygen, the sensor is a
Clark electrode, named after its inventor, Leland Clark. In a Clark
electrode, an electrolyte is placed above the membrane and bridges
the two electrodes. The membrane face of the sensor is placed
against the skin of a patient and a voltage is applied across the
electrodes. Oxygen in the tissue diffuses through the skin, through
the membrane and through the electrolyte to the electrodes where it
is electrochemically reduced by the applied voltage across the
electrodes to cause an electric current to flow between the
electrodes. The current produced by the reduction reaction, which
can be metered and recorded, is a measure of the oxygen in the
tissue.
In the case of carbon dioxide (CO.sub.2), the sensor is a
Stow-Severinghaus electrode, named after its inventors, R.W. Stow
and John Severinghaus. A Stow-Severinghaus electrode (sometimes
called a Severinghaus electrode) is a pH electrode, i.e., it
measures the pH of a solution. When CO.sub.2 is dissolved in the
electrolyte it affects the pH of the solution. A pH electrode
connected to a pH meter can measure the pH. Since pH is
proportional to pCO.sub.2, the pH electrode can also measure
C0.sub.2.
In a Severinghaus electrode, as in the Clark electrode used to
measure oxygen passing through the skin, an electrolyte is placed
above the membrane and bridges the two electrodes. The membrane
face of the sensor is placed against the skin. Unlike the oxygen
sensing Clark electrode, in the Severinghaus electrode used to
measure pCO.sub.2, no voltage is applied across the electrodes.
Carbon dioxide in the blood diffuses through the skin, through the
membrane and through the electrolyte. The effect of the CO.sub.2
dissolving in the electrolyte changes the pH of the electrolyte
thereby inducing a voltage (much like a battery) which is measured
as an indication of the pCO.sub.2 in the body tissue.
It is also known to measure both oxygen and carbon dioxide with a
single sensor probe utilizing a single measuring electrode
(cathode). This results in a compromise since no single measuring
electrode is optimum for use in measuring both oxygen and carbon
dioxide. Hence the use of two separate measuring electrodes, each
optimized for its respective gas, e.g., oxygen and carbon dioxide,
has been found preferable.
Moreover, it is known to facilitate removal and replacement of the
membrane in an oxygen or carbon dioxide electrode sensor probe
through the use of a detachable fixation ring as set forth in U.S.
Pat. No. 4,280,505 to Dali. When a single active electrode is
employed in a single sensor probe to measure oxygen or carbon
dioxide, or both oxygen and carbon dioxide, no problem is presented
with respect to the use of a fixation ring. When two active
electrodes are employed in a single sensor probe to measure oxygen
and carbon dioxide respectively and simultaneously a problem is
presented with respect to the use of a fixation ring. Since carbon
dioxide electrodes differ from oxygen electrodes, and the membrane
material best suited as permeable to oxygen is different from the
membrane material best suited as permeable to carbon dioxide, the
membrane assembly cannot be randomly angularly positioned with
respect to the electrodes as is permissible where a single gas
measuring electrode is used.
The present invention solves the aforementioned problem in
providing for a sensor for monitoring first and second
transcutaneous gases with the use of a single probe having dual
measuring electrodes engaging respective different selectively
permeable seal materials, e.g., membrane materials which can be
mounted by means of a fixation ring that allows the membrane
materials to reproducibly engage their respective measuring
electrodes thereby accomplishing lateral and angular alignment with
respect to eccentrically mounted oxygen and carbon dioxide
electrodes.
SUMMARY OF THE INVENTION
A sensor for monitoring first and second transcutaneous gases at
the surface of the skin including, an electrode housing, a first
electrode mounted in the electrode housing for detecting the first
gas, a second electrode mounted in the electrode housing for
detecting the second gas, a seal supporting housing releasably
mountable on the electrode housing, a selectively permeable seal
mounted on the seal supporting housing, the seal having a first
region permeable to the first gas and a second region permeable to
the second gas, the first and second electrodes being angularly
displaced from an electrode housing index by the same degree to
which the first and second permeable seal regions are respectively
angularly displaced from a seal supporting housing index, and
cooperative interlocking means on the electrode housing and on the
seal supporting housing for positively mounting the seal supporting
housing on the electrode housing with the first region of the seal
in engagement with the first electrode and the second region of the
seal in engagement with the second electrode wherein the indexes
positively limit relative movement therebetween.
It is therefore an object of the invention to provide a sensor for
monitoring first and second transcutaneous gases at the surface of
the skin.
It is another object of the invention to provide a sensor for
monitoring first and second transcutaneous gases at the surface of
the skin by permitting the gases to diffuse through two adjacent
respective regions of a permeable seal, each region being permeable
to a different one of the gases.
It is still another object of the invention to provide a sensor for
monitoring first and second transcutaneous gases at the surface of
the skin wherein the permeable seal is readily removed from and
replaced on the electrode supporting sensor structure.
It is a further object of the invention to provide a sensor for
monitoring first and second transcutaneous gases at the surface of
the skin wherein the seal regions automatically align with their
respective electrodes when replaced on the electrode supporting
sensor structure.
Other and further objects of the invention will be apparent from
the following description of a preferred embodiment of the
invention in which like reference numerals are used to designate
like parts in the various views.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the apparatus of the preferred
embodiment of the invention.
FIG. 2 is a sectional elevation view of the apparatus of the
preferred embodiment of the invention.
FIG. 3 is a plan view of the apparatus of the preferred embodiment
of the invention.
FIG. 4 is a sectional elevation view of a component of the
apparatus of the preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIGS. 1 and 2, there is shown a transcutaneous gas
sensor probe 1 including a housing 3 in which there is mounted a
downwardly extending oxygen electrode 5 and a downwardly extending
carbon dioxide electrode 7, each of which serves as a cathode. A
common anode 9 serves as a reference electrode. The oxygen
electrode 5 can include a solid glass cylindrical rod in which a
platinum wire is axially disposed. The carbon dioxide electrode 7
can include a hollow cylindrical glass tube terminated with pH
glass and partially filled with an electrolyte solution in which a
silver-silver chloride wire is axially disposed.
Respective wire conductors 11 extend from the oxygen electrode 5
and carbon dioxide electrode 7 into a cable 15 and through a bore
in an integral strain relief 13 that extends from the electrode
housing 3. The cable 15 is terminated in a suitable connector (not
shown) for mating with the input of a transcutaneous gas
monitor.
The housing 3 has an enlarged cylindrical upper portion 17 and a
smaller diameter lower portion 19 with threads 21 on its exterior.
A fixation ring 23 which serves as a permeable seal bearing housing
has interior threads 25 for mounting the fixation ring 23 on the
electrode housing 3.
As can be seen in FIG. 4 the fixation ring 23 has a downward facing
circumferential channel 29 surrounding a concentric protuberance 31
having a downward facing planar face 33. A circular ridge 35, the
inner wall of which defines the outer wall of the channel 29
extends axially downwardly beyond the protuberance 31 and upwardly
to a shoulder 37 at which it tapers inwardly as it continues
upwardly to a circular upwardly directed planar face 39. The inner
wall of the channel 29 is defined by the outer wall 43 of the
circular protuberance 31 which tapers downwardly and outwardly at
an angle of about six degrees.
An axial circular bore 45 extends the entire length of the fixation
ring 23 which in the preferred embodiment of the invention is 0.2
inches. Beginning just below, i.e., 0.005 inches, the upwardly
directed planar face 39 in the interior cylindrical wall of the
bore 45 is an integral single pitch thread 46 which in the
preferred embodiment of the invention is 32 threads per inch. The
thread 46 extends downwardly for one half the length of the
fixation ring 23, i.e., for 0.1 inches.
A minimal taper is provided at the start of the thread to form a
convex abutment 47 for engaging a complementary concave abutment 49
at the terminus of the thread 50 on the exterior cylindrical wall
19 of the electrode housing 3. Beneath the thread 46 in the bore 45
of the fixation ring 23 the interior wall 51 of the bore 55 tapers
downwardly and outwardly at an angle of approximately six
degrees.
Referring to FIG. 3, a permeable seal in the form of a compound
circular membrane 55 having a diameter greater than that of the
downwardly directed circular protuberance 31 of the fixation ring
23 is mounted on the underside of the protuberance 31 by means of
an elastomeric 0-ring 61. The circular membrane has a diameter
large enough to extend over the inner wall 43 of the channel 29,
and preferably well into the channel 29.
In the preferred embodiment of the invention, the membrane 29 is
formed from a circular layer of material of one mil thickness sold
under the popular trademark Teflon. Overlying one half of the
Teflon membrane is a semi-circular layer of material of one half
mil thickness sold under the trademark Cuprophane.
The Teflon material is permeable to both oxygen and carbon dioxide.
The cuprophane material absorbs electrolyte and acts as a reservoir
to increase the volume of electrolyte in the vicinity of the carbon
dioxide electrode. In order for accurate measurements to be made,
it is necessary that the oxygen electrode be covered only by the
Teflon-only region 57 of the compound membrane whereas the carbon
dioxide electrode must be covered by the Teflon-cuprophane region
59 as sown in FIG. 3.
The abutment 47 at the beginning of the thread on the fixation ring
or any other fixed point away from the center of the fixation ring
29 can serve as an index for orienting the compound membrane 55 so
that the oxygen electrode 5 is covered only by the Teflon-only
region 57 of the compound membrane while the carbon dioxide
electrode 7 is covered by the Teflon-Cuprophane region 59. This is
done with reference to the angular displacements of the oxygen and
carbon dioxide electrodes 5,7 from a corresponding index point,
e.g., the terminus 49 of the thread 50, on the electrode housing 3.
In the preferred embodiment of the invention, the oxygen and carbon
dioxide electrodes 5,7 are diametrically opposite one another. The
compound membrane 55 is placed over the fixation ring protuberance
31 and oriented so that the angular distance between a radius of
the fixation ring 23 passing through its index point 47 and a
radius passing through the Teflon-only region 57 is equal to the
angular distance between a radius of the electrode housing 3
passing through its index point 49 and a radius passing through the
oxygen electrode 5. Similarly, the angular distance between a
radius of the fixation ring 23 passing through its index point 47
and a radius passing through the Teflon-Cuprophane region 59 is
equal to the angular distance between a radius of the electrode
housing 3 passing through its index point 49 and a radius passing
through the carbon dioxide electrode 7. Once so positioned, the
compound membrane 55 is fixed laterally and angularly in place by
means of the elastomeric 0-ring 61 which is placed over the
compound membrane 55 and protuberance 31. A planar ring 63 can then
be fitted into the channel 29 to form a planar bearing surface for
engaging the skin at the measuring site.
It is to be understood and appreciated that alterations,
modifications and variations of and to the preferred embodiment
described herein may be made without departing from the spirit and
scope of the invention which is defined in the following claims.
For example, although the preferred embodiment of the invention has
been described as utilizing the beginning and terminus of the
fixation ring and electrode housing threads as respective indexes,
another projection or recess, or other visible marking can be
employed. Moreover, the oxygen and carbon dioxide electrodes need
not be on a common diameter provided that they are angularly
displaced from each other.
* * * * *